SSH Failed

I tried to ssh to a new installed server last Friday using Putty, and it gave me the error, “Network error: Connection refused.”. But it had been working when using DHCP!

What happened?

Firewall?

Checking the firewall settings, and it seems to be okay.

sshd?

Checking the ports, and it seems to be okay.

IP Address?

Yes, I typed it correctly.

IP Address!

Finally, I found out that the IP Address has been used by another computer! It took me almost two hours to figure that out. WTF!